1. Field of the Invention
This invention relates to apparatus for and method of operation of a self-cleaning ultrasonic flow sensor that may provide for a longer period of operation before maintenance is required.
2. Background Information
Ultrasonic flow rate measurements are well known and comprise both differential transit time (time of flight) and Doppler approaches. Differential transit time arrangements are exemplified in the inventor's U.S. Pat. Nos. 6,508,134, 6,422,093, and 6,178,827. These instruments typically operate at ultrasonic frequencies of 500 kHz to four megahertz.
Ultrasonic sensors are often used to measure the flow of inadequately treated or untreated water. In these cases materials present in the water commonly settle out on windows used to couple the ultrasonic signals into and out of the flowing fluid. This eventually attenuates and/or distorts the acoustic signals to a degree at which performance is degraded, thus requiring a maintenance operation. Avoiding or forestalling the need for maintenance would thus provide a significant benefit to the flow measurement art.
Ultrasonic cleaners are also well known. These devices generally provide a fluid bath in which an article to be cleaned is immersed. In cleaning operations of this sort, the fluid is commonly insonified at frequencies on the order of tens of kilohertz.